1. Field of the Invention
The present invention generally relates to an exhaust gas cleaning apparatus for cleaning exhaust gas from an internal combustion engine with a catalytic converter. More particularly, the present invention relates to improving an exhaust gas cleaning apparatus by directing exhaust gas into a bypass path equipped with a separate catalytic converter during a period immediately after the engine is cold started during which a main catalytic converter installed in a main exhaust passage is not yet active.
2. Background Information
Most vehicles with an internal combustion engine are provided with an exhaust gas cleaning apparatus. Most exhaust gas cleaning systems are disposed under the floor of a vehicle and include a catalytic converter. When the catalytic converter is arranged in a relatively downstream position from the engine, a sufficient exhaust gas cleaning effect cannot be expected during a period from when the internal combustion engine is cold started until the temperature of the main catalytic converter rises and the main catalytic converter becomes active. Meanwhile, the further upstream a catalytic converter is arranged, i.e., the closer a catalytic converter is arranged to the engine, the service life of the catalytic converter declines due to thermal degradation of the catalyst.
Consequently, some vehicles are provided with an exhaust gas cleaning system that includes a main catalytic converter and a bypass catalytic converter having a smaller capacity than the main catalytic converter. One example of this type of exhaust cleaning system is disclosed in Japanese Laid-Open Patent Publication No. 2005-351088. In this publication, an exhaust gas cleaning apparatus is proposed that has a main exhaust passage with the main catalytic converter and a bypass exhaust passage provided in parallel with an upstream portion of the main exhaust passage. The bypass catalytic converter is provided in the bypass exhaust passage, and a selector valve is provided which allows the flow of exhaust gas to be directed to either the main exhaust passage or the bypass exhaust passage. The selector valve is controlled such that immediately after the engine is cold started, the exhaust gas passes through the bypass exhaust passage and is cleaned by the bypass catalytic converter. Since the bypass catalytic converter is positioned farther upstream than the main catalytic converter and the capacity thereof is smaller than that of the main catalytic converter, the bypass catalytic converter becomes active quickly and starts cleaning the exhaust gas at an early stage.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved exhaust gas cleaning apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.